Public Utilities, Approved Rate, Amount

No definition available.

Name:	njr_PublicUtilitiesApprovedRateAmount
Namespace Prefix:	njr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Site Contingency, Recovery from Third Party of Environmental Remediation Cost, Period

+ References

No definition available.

+ Details

Name:	njr_SiteContingencyRecoveryfromThirdPartyofEnvironmentalRemediationCostPeriod
Namespace Prefix:	njr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable after twelve months or beyond the next operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

+ Details

Name:	us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Best estimate of the reasonably possible loss exposure in excess of the amount accrued for damages pertaining to a specified product.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q2)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_ProductLiabilityContingencyLossExposureInExcessOfAccrualBestEstimate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SiteContingencyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RegulatoryAssetAxis=njr_EnviromentalRemediationCostsExpendedNetOfRecoveriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=njr_RACMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) - USD ($) $ in Thousands			6 Months Ended
	Sep. 09, 2020	Sep. 08, 2020	Mar. 31, 2021	Sep. 30, 2020
Site Contingency [Line Items]
Manufactured gas plant remediation			$ 143,490	$ 150,590
Recovery from third party of environmental remediation cost, period			7 years
Regulatory assets			$ 522,027	$ 527,459
Expended, net of recoveries
Site Contingency [Line Items]
Regulatory assets			37,500
RAC
Site Contingency [Line Items]
Approved rate, amount	$ 9,700	$ 8,500
Minimum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate			143,100
Maximum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate			$ 181,700